1. Technical Field
This disclosure relates to power-line modem networks, and more particularly, to an apparatus and method for providing time synchronization for data in devices of a power-line modem network.
2. Description of the Related Art
Powerline modems communicate by employing a power network as a transmission medium. Powerline modems are employed on a device to set up communication with a master device or controller. Communication carried out on the powerline provides the capability of any plug-in device to communicate on the powerline network. Such devices on the powerline network may share data including digitally compressed video or picture data.
When digitally compressed video data is transmitted over a network, timing synchronization must be maintained between a transmitter of the data and a receiver of the data to display the images at a proper rate. In conventional systems, a timestamp is typically inserted into the data stream. The time stamp provides a reference for the rate in which the images should be displayed to achieve the proper display rate. However, the inclusion of the time stamp in the data stream wastes bandwidth which would otherwise be available for the transmission of data.
There is a trade-off between frequency of insertion and bandwidth wasted. Inserting timestamps more often keeps the clocks better synchronized, but higher frequency rates requires more bandwidth.
Therefore, a need exists for data synchronization between a transmission device and a receiver device in a powerline modem network. A further need exists for synchronization between the devices, which provides a larger amount of available bandwidth and permits synchronization of video, even for asynchronous devices.
A method of synchronization of a powerline modem network for a plurality of devices in accordance with the present invention provides a plurality of devices having a powerline modem and a clock circuit for synchronizing a data rate. The powerline modem permits data transmission between the plurality of devices over a powerline network on data carriers. A synchronization signal is transmitted over the powerline network. The synchronization signal includes a carrier operating at a frequency different from the data carriers and provides each of the plurality of devices a time reference to synchronize the data rate.
A powerline network with data synchronization in accordance with the present invention includes a plurality of devices each having a powerline modem and a clock circuit for synchronizing a data rate. The powerline modem permits data transmission between the plurality of devices over the powerline network on data carriers. A master device has a powerline modem coupled to the powerline network and includes a clock transmission circuit. The clock transmission circuit generates a synchronization signal over the powerline network, and the synchronization signal includes a carrier operating at a frequency different from the data carriers. The synchronization signal provides each of the plurality of devices a time reference to synchronize the data rate.
In other embodiments, transmitting the synchronization signal over a plurality of carriers operating at a frequency different from the data carriers is preferable. The step of transmitting a synchronization signal may include the step of sending a current timestamp to the plurality of devices. Each of the plurality of devices then sounds off during an assigned time slot, and an error offset is determined between the assigned time slot and the sounding off of the device. A correction factor is transmitted to the plurality of devices to correct synchronization of the clock circuit of the devices, which may include error offsets.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.